A valve apparatus includes a fluid-bearing module and an actuation module. The fluid-bearing module includes a substrate and a channel formed in the substrate, the channel having microfluidic dimensions. The actuation module is detachably secured to the fluid-bearing module and includes a heating/cooling element adjacent to the channel. The heating/cooling element is controllable to generate or absorb sufficient energy to cause the a material in the valve apparatus to transition from a solid phase to a liquid phase, or from a solid phase to a liquid phase, or to expand or contract, thereby providing a phase-change valve.